Yet another example of why we should get rid of this archaic slice of nonsense - why use RPS when you would have perfectly accurate and more relevant pressure settings (Both the Culdrose and the St Mawgan QNH's).
My preferred answer would be "C" - that way you would know your altitude relevant to obstacles in the area (the main reason for using an altimeter) AND it would tell you exactly how far above the St Mawgan MATZ you would be (4000ft - 3000ft - EGDG Aerodrome elevation).